Modern electronic appliances such as computers have many hundreds of integrated circuits and other printed circuit boards. Many of these components generate heat during normal operation. Components that are relatively large, or that have a relatively small number of functions in relation to their size, as for example individual transistors or small scale integrated circuits, usually dissipate all their heat without a heat sink. The large physical size of such components, especially as compared with their active portions, limits their density on a circuit board sufficiently so that there is enough room for any heatsinks that might be needed. Accordingly, any component that needs assistance in dissipating heat can have a heatsink of its own.
The term "heatsink" as used herein generally refers to a passive device, for example an extruded aluminum plate with a plurality of fins, the heatsink being thermally coupled to an electronic component to absorb and dissipate heat into the air by convection.
As the state of the electronic arts has advanced, components have become smaller and smaller, to the extent that many thousands of them are now combined into a single integrated circuit chip. In addition, components are being made to operate faster and faster to provide the computing power that is increasingly being required of computers and other electronic devices. As the operating speed increases, so does the amount of heat which the components must dissipate. These factors have made it more difficult for many components to dissipate the heat they generate without the assistance of external heat sinks. At the same time, increasing component density has made it impractical to provide individual heat sinks for the increasing numbers of components that need them. Accordingly, it has become necessary for many components to share one heat sink.
One widely-used method of increasing the speed of an electronic circuit is to reduce the lengths of connecting wires. In part, this is being done by abandoning the older practice of enclosing each integrated circuit chip in a separate package in favor of mounting many chips next to each other on a single substrate. Such an assembly of chips and substrate is commonly referred to as a multi-chip module ("MCM"). The chips on an MCM are too small, and usually must be located too near one another on the MCM, to permit the use of separate heat sinks for the individual chips. Accordingly, in order to dissipate the heat generated by the chips on an MCM, it is often necessary to use a single heatsink for a large group of chips or components.
Accordingly, a heatsink should be capable of high convection of heat into the surrounding air. Heatsinks for electronic components have achieved this ability in the past by having a multitude of fins physically connected to a heatsink base which is then thermally coupled to a substrate having heat generating components. The manufacturing process for heatsinks is difficult and expensive as the individual fins must be connected to a base with a matching coefficient of heat transfer or conductivity. Without a proper thermal conductivity match, the heat is not effectively conveyed to the fins and dissipated into the air from the heatsink base.
To avoid thermal mismatches, a heatsink and the related fins might be extruded as one single piece, thereby eliminating any attachment process of the fins. Such extrusions, however, provide lower aspect ratios, e.g. 4-5, and hence lower surface area across the array of fins. The aspect ratio is defined as the height of the fin divided by the gap between each subsequent fin, or height/gap. Due to the low surface area, the extruded heatsinks require higher air velocities than that required for high density, high aspect ratio heatsinks. Relatedly, extruded heatsinks require higher tangential velocities of air, e.g. 4 to 5 meters/second (m/s), flowing over the fins in order to remove sufficient heat. To provide higher air velocities, larger more cumbersome fans, or fans that require more power to operate, are generally needed. Other formation methods that can produce higher aspect ratios are, but generally prove to be even more expensive. Such methods include, for instance, machining fins via a saw cut, or brazing fins onto the part.
Yet another expensive and time consuming process for achieving a thermal match involves physically bonding the fins to a base structure. Ideally, a heatsink will employ as many fins as possible to maximize the surface area exposed to the surrounding air. However, the time and expense involved in bonding the individual fins leads to a trade-off between the aspect ratio and the cost of constructing the overall heatsink. Heatpipes can also be incorporated into heatsinks to convey heat from an electronic component to the fins for dissipation of the heat into the air. Incorporation of such heatpipes, however, can require exacting manufacturing tolerances in order to provide a low thermal resistance between the heatpipe and the heatsink material.
As a result, a low-cost, high aspect ratio heatsink assembly is needed for application to heat producing electronic components. Heatpipes should be incorporated at minimum cost, but with maximum thermal efficiency between the assembly parts. The heatsink assembly should provide a effective heatsink and means of application so that sufficient "wetting" of the fin surfaces is achieved, with relatively low airflow being required over the fins.